The present invention relates to a traction drive with a converter and a permanent-excited synchronous motor, wherein the converter includes a machine-side pulsed inverter.
Conventional traction wheels of rail cars include asynchronous drive motors that are powered by traction drives with pulsed inverters. These traction drives can also be operated as a generator brake in travel and braking mode. A wheel set must have a reliable fail-safe brake so that the motor car can maintain the approved braking distance even if the pulsed inverter malfunctions. Examples of fail-safe brakes are mechanical brakes, for example, disk brakes, shoe brakes and/or electromagnetic rail brakes.
The brake system of an ICE 2/2 train set is described in section 4.3 of the publication “Neue IntercityExpress Triebzüge für die deutsche Bahn” (New InterCity-Express-Trains for the German Railways), printed in the German-language publication “eb—Elektrische Bahnen”, Vol. 93, 1995, No.1/2, pp. 15 to 24. Such train sets have, in addition to the generator brake of the three-phase asynchronous drive with power line return feed, an air disk brake in both the traction wheels and the track wheels. The brake disks on the track wheels are axle-mounted brake disks, with the brake disks associated with the traction wheels having sintered brake pads. The electronic brake control is combined with the electro-pneumatic control, so that the speed does not have to be restricted if the electronics fails. Preferably, the generator brakes are activated first, and only afterwards are the mechanical brakes activated.
The mechanical brakes disadvantageously represent a complex system prone to malfunction, that can be quite expensive and require frequent maintenance. Moreover, a malfunction in the anti-skid protection can immediately cause flat spots on the wheel sets, which may require reprofiling the wheels at a significant expense.
The European Pat. No. 0 704 961 describes a device for braking a permanent-excited synchronous motor of a lift, wherein the stator windings can be connected with brake resistors via a switch. A frequency converter supplies electric power to the stator winding of the permanent-excited synchronous motor. Due to the small synchronous inductance, each of the add-on brake resistors must have a nonlinear resistance value, whereby the resistance increases with increasing voltage. This nonlinear resistance characteristic ensures a minimum acceptable deceleration rate. The braking power and the current flowing through the brake resistor become large when the stator windings of the permanent-excited synchronous motor supply current through the brake resistors and the motor operates at a very high-speed.
It would therefore be desirable and advantageous to equip a rail car with traction wheels that do not require a mechanical brake and are able to specifically prevent flat spots on wheel rims without the need for a nonlinear resistor.